An American Eagle Embraer E170 jet passes in front of the iconic Hollywood sign while on final approach to Los Angeles International Airport on Nov. 8, 2015. Jeremy Dwyer-Lindgren, Special for USA TODAY

The skyline of New York. American counts its operations operations at JFK and LaGuardia airports as a combined hub, though the airports are separated by a considerable cab ride during normal traffic conditions.LaGuardia was American's eighth-busiest hub (by passengers) in 2015. JFK was ninth. Mark Lennihan, AP

American Airlines tightened its policy Monday for passengers bringing emotional-support animals on flights. The animals must fit at the passenger's feet and not block an aisle, and the passenger much provide documentation certifying the need for the animal.(Photo: mauinow1, Getty Images/iStockphoto)

American Airlines joined other major airlines Monday in restricting emotional-support animals allowed to fly with passengers.

Airlines decided to revise their own rules after a Transportation Department panel was unable to reach a compromise in 2016. Emotional-support animals fell under a looser definition than trained service animals, such as for the blind or deaf, while still traveling for free in the cabin rather than being shipped in cargo.

Delta said its changes came as the airline carried about 250,000 animals last year that were increasingly misbehaving by wandering the cabin, defecating or even biting passengers. A comfort dog bit a passenger in the face while a flight boarded last June.

United's change came after a woman tried to bring a peacock with her on a flight. But United began reviewing its policy in 2017 after noticing a jump in comfort animals on flights to 76,000 from 43,000 the year before, and “a significant increase in onboard incidents.”

Starting July 1, American will require passengers to notify the carrier about a comfort animal 48 hours before a flight, and then sign a waiver stating the need for the animal.

In order for an animal to qualify, the passenger must provide a letter from a mental-health professional describing the mental or emotional disability that shows the need for the animal, and proof of the professional’s licensing.

Comfort animals must fit at a passenger’s feet without occupying a seat or blocking an aisle, under the policy. The animals must be tethered by a leash or harness at all times and won’t be permitted in the cabin if they behave badly, such as by growling, lunging or attempting to bite people, the airline said.

“We’re tightening things down a little bit,” said Suzanne Boda, American’s senior vice president for Los Angeles, who helped develop the policy. “We want to make sure that the safety of everyone, including service animals, is protected.”

American also prohibited a dozen types of animals from being considered emotional-support animals, including amphibians, ferrets, rodents and non-household birds.

The airline developed the policy in consultation with groups including the American Association of People with Disabilities, Paralyzed Veterans of America, American Council for the Blind and My Blind Spot.

Albert Rizzi, CEO of My Blind Spot, who has worked with American for four years developing policies for people with disabilities, said the changes for emotional-support animals are intended to clearly define when the animals are needed for ailments that aren’t obvious such as detecting an owner’s stress or a diabetic’s fluctuations in blood sugar.

“A lot of people tend to try to skirt the polices and protocols that are in place,” Rizzi said. “It’s hard to discern the difference between people passing off a pet as an emotional support dog versus a legitimate service animal that is there to mitigate a disability.”